1. Field of the Invention
This invention relates in general to phase regulating circuits of the delayed lock loop type.
2. Description of the Prior Art
Phase follow-up regulating circuits operating according to the delayed lock loop principle DLL for phase coherent synchronization of the pulse sequence of a receiving pseudo-random generator which is controlled by a pulse train oscillator by the incoming pulse sequence are known. The incoming pulse sequence might be modulated on a carrier frequency of an identical pseudo-random generator at the transmitting end and two identical signal channels are provided each of which includes a mixer which also receives the output of the pseudo-random generator and each of which includes a following network. The outputs of the network are supplied to a difference forming device and each of the inputs receive the incoming signal and the output of the difference forming device is supplied through a loop filter and controls a pulse train oscillator which supplies an output to the pseudo-random generator.
Phase follow-up regulating circuits of this type are required particularly at the receiving end of information transmission systems particularly where for coding or for reducing the interference or for multiple access SSMA pseudo-random generators at the transmitting and receiving ends are used. In such systems, to restore the transmitted data requires that a phase coherent synchronization occur at the receiver so that the pseudo-random generator is synchronized with the pseudo-random generator at the transmitting end to allow demodulation of the intelligence. The phase follow-up regulating circuits are the basic element of an auto-correlation receiver in which the incoming pulse sequence is compared with the output of the pseudo-random generator at the receiver and the phase coherence of the two pulse sequences is identified by a d.c. voltage occurring at the output.
For regulating purposes, it is effective and desirable that the output signal should be of a form which passes through zero linearly in the region of the synchronization point. Systems such as disclosed in the article "IEEE Transactions on Space Electronics and Telemetry" 1963, pages 1 to 8 are known. However, in the systems of the prior art, the two separate channels of the receiver generally are non-linear having different gains which causes the zero point to shift due to the asymmetry of the two channels.